The present invention relates to nucleic acid molecules encoding R1-protein from wheat and derivatives and parts thereof, said R1-protein, processes for the production of said R1-protein, transgenic plant cells and plants comprising said nucleic acid molecules, the transgenic plant cells and plants comprising said nucleic acid molecule, and the modified starch obtainable from said transgenic plant cells and plants.
The polysaccharide starch constitutes one of the most important storage substances in plants. Starch is widely used for the production of foodstuffs and plays also a significant role as a regenerative raw material in manufacturing of industrial products. In order to use starches in many different technical areas a large variety of optionally modified starches is required in order to meet the varying needs of the processing industry.
Although starch consists of a chemically homogeneous basic component, namely glucose, it does not constitute a homogeneous raw material. It is a complex mixture of molecules which differ in their degree of polymerization and degree of branching of the glucose chains: Amylose-type starch is a basically unbranched polymer consisting of xcex1-1,4-glycosidically branched glucose molecules, whereas amylopectin-type starch is a mixture of branched glucose chains, comprising additionally xcex1-1,6-glycosidic interlinkings.
The molecular structure of starch mainly depends on its degree of branching, the amylose/amylopectin ratio, the average chain-length, chain lenght distribution, and degree of phosphorylation, further determining the functional properties of the starch and the aequous solutions thereof. Important functional properties of the starch, resp., the aequous solutions thereof are, e.g., solubility, tendency to retrogradation, capability of film formation, viscosity, pastification (binding and gluing) properties, and cold resistance. Additionally, the size of the starch granules may also determine the suitability of the starch for particular applications.
Since starch is often adapted by chemical and/or physical modification in order to meet the requirements of industry, there is a great need for the provision of modified starches which would render plant cells or plant parts containing modified starch more suitable for industrial processing, e.g., the production of foodstuff or technical products. Therefore, it is desired to avoid chemical and/or physical modification, which is time-consuming and expensive and to provide plants which synthesize a starch which meets more closely the demands of the starch processing industry.
Conventional methods for the preparation of modified plants which produce modified products, e.g., by classical breeding and/or the production of mutants, are limited to the use of homologous genes and are not always satisfying. Particularly in wheat, it is difficult to prepare a stable mutant by classical breeding due to the polyploidity of wheat (tetra- or hexaploidity). However, a wheat mutant producing waxy-type starch (amylose-free starch) was recently achieved by breeding methods (Nakamura et al., Mol. Gen. Genet. 248 (1995), 253-259).
A further alternative is the preparation of transgenic plants which comprise nucleic acid molecules suitable to modify plant starch metabolism in order to synthesize a modified starch. Such plants are produced by means of recombinant molecular biological techniques and the introduction of homologous and/or heterologous nucleic acid molecules (e.g., coding regions, regulatory elements, introns), which interfere in starch metabolism. However, the application of recombinant molecular biological techniques requires the availability of suitable nucleic acid which participate directly or indirectly (e.g., cosuppression, anti-sense-technology, generation of protein or ribozyme) in starch metabolism or starch biosynthesis (i.e., synthesis, modification and/or degradation of starch) with respect to quantity and/or quality of the starch.
Numerous genes are involved in starch metabolism. Therefore, a large number of genes encoding, e.g., branching enzymes, debranching enzymes, isoamylases, starch synthetases, ADP-glucose-pyrophosphorylases, have been used to modify starch metabolism in plants.
R1 proteins are involved in starch metabolism, especially with respect to the degree of phosphorylation of the starch and therefore, suitable to modify starch synthesis. In particular, R1-proteins and genes encoding R1-proteins derived from a number of plant species are known, i.e., potato from WO 97/11188-A1 and Lorberth et al., Nature Biotechnology 16 (1998), 473-477), maize from WO 98/27212-A1, rice from Sakaki et al., EMBL database entry Accession No. C 71741 (Sep. 19, 1997), and arabidopsis, ginger, mosses, cattail (Typha latifolia), and soybean from WO 99/53072-A1.
However, the presence of an R1-protein in wheat plants was not shown, corresponding nucleic acid molecules were not identified. Furthermore, the known nucleic acid molecules encoding R1-proteins are not always satisfying or suitable for the genetic engineering or the in vivo mutagenesis of wheat plants in order to modify wheat starch biosynthesis and/or metabolism.
Therefore, the problem to be solved by the present invention is to provide nucleic acid molecules encoding R1-protein derived from wheat and methods which allow the modification of starch metabolism in plants, especially in wheat plants in order to provide a modified starch, which differs from starch naturally synthesized with respect to its physical and/or chemical properties, especially wheat starch, exhibiting improved features, in particular for application in food and/or non-food industry.
These problems are solved by the embodiments of the present invention as claimed.
Therefore, the present invention relates to nucleic acid molecules encoding R1-protein comprising an amino acid sequence according to Seq. ID No. 2 and Seq. ID No. 9 or derivative or part thereof according to the cDNA insert of plasmid pTaR1-11 (DSM No. 12810) and plasmid RS26-88 (DSM No. 1351 1). Said R1-protein of the invention is involved in starch metabolism and is involved directly or indirectly in starch biosynthesis of wheat with respect to the degree of phosphorylation.
Within the meaning of the present invention, the term xe2x80x9cderivativexe2x80x9d regarding the R1-protein (polypeptide, amino acid sequence) of the invention encompasses a polypeptide derived from Seq ID No. 2 comprising about at least 60-79 amino acid radicals, preferably at least 80, more preferred at least 90, in particular at least 100, and most preferably about 101-111 amino acid radicals selected from the group of amino acid radicals consisting of 1E, 2V, 3V, 5G, 6L, 7G, 8E, 9T, 10L, 11V, 12G, 13A, 14Y, 15P, 16G, 17R, 18A, 20S, 21F, 23C, 24K, 25K, 27D, 28L, 30S, 31P, 34L, 35G, 36Y, 37P, 38S, 39K, 40P, 41I, 42G, 43L, 44F, 45I, 48S, 49I, 50I, 51F, 52R, 53S, 54D, 55S, 56N, 57G, 58E, 59D, 60L, 61E, 62G, 63Y, 64A, 65G, 66A, 67G, 68L, 69Y, 70D, 71S, 72V, 73P, 74M, 75D, 77E, 80V, 81V, 83D, 84Y, 87D, 88P, 89L, 90I, 92D, 95F, 96R, 99I, 100L, 101S, 103I, 104A, 105R, 106A, 107G, 108H, 109A, 110I, 111E, 112E, 113L, 114Y, 115G, 116S, 117P, 118Q, 119D, 121E, 122G, 123V, 124V, 126D, 127G, 128K, 129I, 130Y, 131V, 132V, 133Q, and 134T and comprising at least 1, preferably 2, and more preferred 3 of the amino acid radicals selected from the group consisting of 76V, 93S, and 97N of the amino acid radicals (hereinbefore indicated by single letter code) as specified in Seq ID No. 2.
Within the meaning of the present invention, the term xe2x80x9cpartxe2x80x9d regarding the R1-protein (polypeptide, amino acid sequence) of the invention encompasses a poly- or oligopeptide consisting of about at least 10-19, preferably at least 20, more preferably at least 40, in particular preferably at least 80, and most preferably about 100-140 of the amino acid radicals of the R1-protein or derivative thereof according to the invention.
The present invention further relates to nucleic acid molecules comprising a nucleic acid molecule derived from Seq. ID No. 1 and Seq. ID No. 9 or derivatives or parts thereof, the 672 bp EcoR I/Kpn I insert of plasmid pTa R1-11 (DSM No. 12810) or derivatives or parts thereof, in particular the coding region (nucleotides 1-449) of Seq. ID No. 1 or derivatives or parts thereof, especially the coding region of the insert of plasmid pTa R1-11 (DSM No. 12810) and the coding region of plasmid RS26-88 (DSM No. 13511) or derivatives or parts thereof.
Within the meaning of the present invention, the term xe2x80x9cderivativexe2x80x9d regarding the nucleic acid molecule (nucleotide sequence, or polynucleotide) of the invention encompasses a polynucleotide comprising about at least 150-209 nucleotides, preferably at least 210, more preferred at least 240, in particular at least 270, and most preferably about 280-294 nucleotides selected from the group of nucleotides consisting of
(a) 1C, 3G, 4A, 6G, 7T, 8G, 9G, 10T, 12A, 15G, 16G, 18C, 19T, 20T, 21G, 22G, 24G, 25A, 27A, 28C, 30C, 31T, 33G, 34T, 36G, 37G, 38A, 39G, 40C, 42T, 43A, 44T, 45C, 46C, 48G, 49G, 51C, 52G, 53T, 54G, 55C, 58T, 59G, 60A, 61G, 63T, 64T, 67T, 69T, 70G, 72A, 73A, 75A, 76A, 77A, 79A, 81G, 82A, 84C, 85T, 88A, 89C, 90T, 91C, 92T, 93C, 94C, 97A, 100T, 103T, 105G, 106G, 107T, 108T, 109A, 110C, 111C, 112C, 114A, 115G, 116C, 117A, 118A, 120C, 121C, 123A, 124T, 126G, 127G, 129C, 130T, 132T, 133T, 134C, 135A, 136T, 137A, 138A, 144T, 145C, 147A, 148T, 149C, 150A, 151T, 152C, 153T, 154T, 155C, 156C, 157G, 159T, 160C, 162G, 163A, 165T, 166C, 168A, 169A, 171G, 172G, 174G, 175A, 177G, 178A, 181T, 182G, 183G, 184A, 185A, 186G, 187G, 188T, 189T, 190A, 192G, 193C, 195G, 196G, 198G, 199C, 201G, 202G, 205T, 207T, 208A, 210G, 211A 213A, 214G, 215T, 216G, 217T, 219C, 220C, 222A, 223T, 224G, 225G, 226A, 227T, 228G, 230G, 231G, 232A, 234G, 235A, 238A, 240G, 241T, 242T, 243G, 244T, 245A, 247T, 249G, 250A, 252T, 253A, 256C, 259C, 261G, 262A, 263C, 264C, 265C, 268T, 270A, 271T, 276G, 277A, 281T, 285T, 286T, 287C, 288C, 289G, 295C, 296A, 297A, 298T, 299C, 300C, 301T, 303T, 304C, 306A, 308C, 309A, 310T, 312G, 313C, 315C, 316G, 318G, 319C, 320T, 321G, 322G, 324C, 325A, 327G, 328C, 330A, 331T, 332C, 333G, 334A, 335G, 336G, 337A, 338G, 339C, 340T, 342T, 343A, 344T, 345G, 346G, 348T, 349C, 351C, 352C, 354C, 355A, 357G, 358A, 361T, 363G, 364A, 365G, 366G, 367G, 369G, 370T, 371A, 372G, 373T, 374G, 375A, 377G, 378G, 379A, 380T, 381G, 382G, 384A, 385A, 387A, 388T, 390T, 391A, 393G, 394T, 396G, 397T, 399C, 400A, 401G, 402A, 403C, 404A, 406A, 407C, 408C, 409A, 410C, 411A, 412G, 413A, 414T, 415G, 416T, and 419T as specified in Seq. ID No. 1, and
(b) comprising about at least 15-19 nucleotides, preferably at least 20, more preferred at least 25, in particular at least 27, and most preferably about 30-32 nucleotides selected from the group consisting of
17A, 23A, 50C, 56C, 65C, 68G, 71T, 104G, 113T, 143G, 159C, 161A, 167T, 191C, 203G, 206G, 218C, 221T, 229T, 233A, 248C, 251C, 257G, 269C, 272C, 279T, 280C, 290G, 326C, 341 C, 347G, 350A. 353A, 359T, 383G, 392C, and 405T as specified in Seq. ID No. 1.
It is expressly stated that the numbering of the elements of the sequences (on one hand nucleic acid sequence and on the other amino acid sequence) shall not be understood as a fixed or limiting definition. The numbering shall merely provide the information of the positions of the sequence elements to each other in relative terms and is therefore a reference.
Furthermore, the term xe2x80x9cderivativexe2x80x9d regarding the nucleic acid molecule encoding an R1-protein according to the invention encompasses a nucleic acid molecule which is different from Seq. ID No. 1 and/or Seq ID No. 9 by addition, deletion, insertion or recombination of one or more nucleotides and fulfills the definition as given above under (b).
Additionally, the term xe2x80x9cderivativexe2x80x9d regarding the nucleic acid molecule encoding an R1-protein according to instant invention encompasses a complementary or reverse complementary polynucleotide of the nucleic acid molecule according to the invention or parts thereof. Furthermore, the term xe2x80x9cderivativexe2x80x9d regarding the nucleic acid molecule encoding an R1-protein according to instant invention comprises a polynucleotide hybridizing with the nucleic acid molecule according to the invention or parts thereof, which fulfills the definition as given above under (b).
The term xe2x80x9chybridizationxe2x80x9d denotes, for the purposes of the present invention, a hybridization under conventional hybridization conditions, preferably under stringent conditions as described, for example, by Sambrook et al., Molecular Cloning, A Laboratory Manual, 2nd Edition (1989) Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y.).
Especially preferably, xe2x80x9cspecific hybridizationxe2x80x9d means the following conditions: Hybridization buffer: 2xc3x97SSC; 10xc3x97Denhardt solution (Ficoll 400+PEG+BSA; ratio 1:1:1); 0.1% SDS; 5 mM EDTA; 50 mM Na2HPO4; 250 xcexcg/ml herring sperm DNA; 50 xcexcg/ml tRNA; or 0.25 M sodium phosphate buffer pH 7.2; 1 mM EDTA; 7% SDS at a
Hybridization temperature of T=55 to 68xc2x0 C.,
Wash buffer: 0.2xc3x97SSC; 0.1% SDS and
Wash temperature: T=40 to 68xc2x0 C.
The molecules which hybridize with the nucleic acid molecules according to the invention or with the nucleic acid molecules to be suitably employed according to the invention also encompass parts, derivatives and allelic variants of the nucleic acid molecules according to the invention or the nucleic acid molecule to be suitably employed in accordance with the invention.
The term xe2x80x9cderivativexe2x80x9d means, within the context of the present invention, that the sequences of these molecules differ from the sequences of the nucleic acid molecules according to the invention or to be suitably employed in accordance with the invention in one or more positions and exhibit a high degree of homology to these sequences. Homology means a sequential identity of at least 60%, preferably over 70%, and especially preferably over 85%, in particular over 90% and very especially preferably over 95%. The deviations relative to the nucleic acid molecules according to the invention or to the nucleic acid molecules to be suitably employed in accordance with the invention may have originated by means of one or more deletions, substitutions, insertions (addition) or recombinations.
Furthermore, homology means that a functional and/or structural equivalence exits between the nucleic acid molecules in question and the proteins encoded by them. The nucleic acid molecules which are homologous to the molecules according to the invention or to the molecules to be suitably employed in accordance with the invention and which constitute derivatives of these molecules are, as a rule, variations of these molecules which constitute modifications which exert the same, a virtually identical or a similar biological function. They may be naturally occurring variations, for example sequences from other plant species, or mutations, it being possible for these mutations to have occurred naturally or to have been introduced by directed mutagenesis. The variations may further be synthetic sequences. The allelic variants may be naturally occurring variants or else synthetic variants or variants generated by recombinant DNA technology.
The term xe2x80x9cpartxe2x80x9d regarding the nucleic acid molecule encoding an R1-protein according to instant invention encompasses a poly- or oligonucleotide consisting of about at least 30-99, preferably at least 100, more preferably at least 200, in particular at least 300, and most preferably at least 400 of the nucleotides of the nucleic acid molecule encoding an R1-protein or derivative thereof according to the invention. The term xe2x80x9cpartxe2x80x9d is not limited to portions of the nucleic acid molecules which are long enough to encode a functionally active portion of the R1-protein as described.
In a preferred embodiment of instant invention, the terms xe2x80x9cderivativexe2x80x9d and/or xe2x80x9cpartxe2x80x9d according to instant invention encompass a polynucleotide, resp., poly- or oligopeptide as defined above, which exhibits functional and/or structural equivalence of the R1-gene (i.e., the nucleic acid molecule encoding R1-protein), resp., R1-protein derived from wheat. The the term xe2x80x9cfunctional and/or structural equivalencexe2x80x9d generally means the same, an equivalent or a similar function of the resp. molecule of the invention, especially biological function. The term xe2x80x9cpartxe2x80x9d is, however, not limited to portions of the said nucleic acid molecule, which are sufficient to encode a functionally active portion of the said protein.
The R1-proteins encoded by the nucleic acid molecules according to the invention may exhibit certain common characteristics, e.g., enzyme activity, molecular weight, immunologic reactivity, conformation, mobility in gel electrophoresis, chromatographic characteristics, sedimentation coefficients, solubility, spectroscopic properties, stability, pH-optimum and/or temperature-optimum of the enzymatic activity, etc.
The nucleic acid molecule of the invention may be isolated from, e.g., natural sources, prepared by methods of genetic engineering or molecular biology (e.g., PCR) or produced by means of chemical synthesis. The nucleic acid molecule of the invention is preferably a DNA or RNA molecule, e.g., a cDNA or genomic DNA molecule. Optionally, the nucleic acid molecule of the invention comprises one or more intervening sequences (introns).
In another preferred embodiment the nucleic acid molecule of the invention comprises one or more regulatory elements that ensure the transcription and synthesis of an RNA molecule in a prokaryotic and/or eukaryotic cell, preferably in a plant cell.
The nucleic acid molecule according to the invention is suitable in order to modify starch biosynthesis/metabolism in a cell, preferably in a plant cell by means of sense expression of the nucleic acid molecules of the invention, antisense expression of the nucleic acid molecules of the invention, expression of a suitable ribozyme, cosuppression or in vivo mutagenesis.
Therefore, the invention relates also to the use of the nucleic acid molecule of the invention, in particular a DNA molecule, which allows the synthesis of a translatable or a non-translatable mRNA molecule (sense- or anti-sense-, co-suppression effect or ribozyme) in a cell or a plant cell which modifies the R1-protein expression level.
Generally, the use of the nucleic acid molecules of the invention is suitable in any plant species. However, monocotyledonous and dicotyledonous plants are preferred, in particular crop plants and most preferred starch-storing plants, e.g., rye, barley, oats, wheat, millet, sago, rice, maize, peas, wrinkled peas, cassava, potato, tomato, oilseed rape, soy bean, hemp, flax, sunflower, cow-pea, arrowroot, clover, ryegrass, or alfalfa, in particularly potato, maize, rice or wheat plants.
The method of co-suppression is well known to the person skilled in the art (Jorgensen, Trends Biotechnol. 8 (1990), 340-344, Niebel et al., Curr. Top. Microbiol. Immunol. 197 (1995), 91-103, Flavell et al., Curr. Top. Microbiol. Immunol. 197 (1995), 43-56, Palaqui and Vaucheret, Plant. Mol. Biol. 29 (1995), 149-159. Vaucheret et al., Mol. Gen. Genet. 248 (1995), 311-317 and de Borne et al., Mol. Gen. Genet 243 (1994), 613-621.
In a further embodiment the present invention relates to a DNA molecule encoding an RNA molecule exhibiting ribozyme activity which specifically cleaves transcripts of the DNA molecule of the invention. Ribozymes are catalytically active RNA molecules capable of cleaving RNA molecules and specific target sequences. By means of recombinant DNA techniques it is possible to determine the specificity of a ribozyme with respect to the nucleic acid molecule of the invention. In order to prepare a DNA molecule encoding a ribozyme which specifically cleaves a transcript of a DNA molecule of the invention, e.g., a DNA sequence (DNA molecule) encoding a catalytic domain of a ribozyme is bilaterally linked to a DNA sequence of the invention. A nucleic acid sequence encoding the catalytic domain is, e.g., the catalytic domain of the satellite DNA of the SCMo virus (Davies et al., Virology 177 (1990), 216-224) or the satellite DNA of the TobR virus (Steinecke et al., EMBO J. 11 (1992), 1525-1530; Haseloff and Gerlach, Nature 334 (1988), 585-591). The DNA sequence flanking the catalytic domain is preferably the DNA molecule of the invention or part thereof, which shall serve as a target. The general principle of the expression of ribozymes and the method is described in EP-B1 0 321 201. The expression of ribozymes in plant cells is further described in Feyter et al. (Mol. Gen. Genetic. 250 (1996), 329-338).
A reduction of the activity of the R1-protein of the invention in a plant cell can also be achieved by the method of xe2x80x9cin vivo mutagenesisxe2x80x9d. Hereby, a hybrid RNA/DNA oligonucleotide (chimeroplast) is introduced into a cell (Kipp et al., Poster Session at the 5th International Congress of Plant Molecular Biology, Sep. 21 to 27, 1997, Singapore; Dixon and Arntzen, meeting report on xe2x80x9cMetabolic Engineering in Transgenic Plantsxe2x80x9d Keystone Symposia, Copper Mountain, Colo., USA, TIBTECH 15 (1997), 441-447; WO 95/15972-A1; Kren et al., Hepatology 25 (1997), 1462-1468; Cole-Strauss et al., Science 273 (1996), 1386-1389).
Therefore, yet another object of the invention is a plant, preferably a wheat plant, exhibiting an altered activity of the R1-protein according to the invention obtainable by in vivo mutagenesis.
Furthermore, the invention relates to a vector, especially a plasmid, cosmid, virus, bacteriophage and the like, suitable in genetic engineering, comprising a nucleic acid molecule (e.g., DNA and/or RNA) of the invention, in particular a vector suitable in genetic engeneering of bacteria and/or plants. The term xe2x80x9cvectorxe2x80x9d means a suitable vehicle known to the skilled artisan, which allows the targeted transfer of single or double-stranded nucleic acid molecules into a host cell, e.g., a DNA or RNA virus or virus fragment, a plasmid which is suitable for the transfer of a nucleic acid molecule into a cell in the presence or absence of regulatory elements, metal particles as employed, e.g., in the particle-gun method, but also a nucleic acid molecule which can be directly introduced into a cell by chemical and/or physical methods.
In a further embodiment the invention relates to a transgenic host cell, which is transformed and/or recombinantly manipulated by a nucleic acid molecule or a vector according to the invention, in particular a transgenic prokaryotic or eukaryotic cell, and more preferably a transgenic bacterial or a plant cell. The transgenic host cell according to the invention, especially the transgenic bacterial or plant cell contains one or more nucleic acid molecules of the invention, which are stably integrated into the genome of said cell, preferably not at the homologous genomic locus, resp., not at the location of the naturally occurring gene within the genome. The transgenic cells according to the invention may be identified by Southern Blot, Northern Blot and/or Western Blot analysis.
Additionally, the present invention relates to a transgenic cell, which is derived from the transgenic host cell of the invention and/or the descendants thereof containing a nucleic acid molecule or a vector according to the invention.
By provision of the nucleic acid molecule and/or the vector of the invention a transgenic plant cell or plant is prepared by means of recombinant DNA techniques comprising a nucleic acid molecule and/or a vector according to the invention, in particular a monocotyledonous or dicotyledonous plant cell or plant, preferably a crop plant cell or a plant, in particular a plant cell or plant selected from the group consisting of a potato, maize, oat, rye, barley, wheat, pea, rice, millet, wrinkled peas, cassava, sago, tomato, oilseed rape, soy bean, hemp, flax, sunflower, cow-pea, arrowroot, clover, ryegrass, alfalfa, and maniok.
The transgenic plant cell or plant of the invention synthesizes a modified starch which differs from the starch synthesized in a wildtype (non-transformed) plant with respect to structure and/or physical and/or chemical properties. By the methods of genetic engeneering and/or molecular biology, a vector and/or a nucleic acid molecule of the invention is introduced into a plant cell, preferably linked to one or more regulatory elements, which ensure transcription and/or translation in said plant cell. Optionally, the resulting transgenic plant cell is subsequently regenerated to a whole plant.
Therefore, the present invention relates to a transgenic plant cell, in particular a monocotyledonous or dicotyledonous plant cell, preferably, a potato, maize, oat, rye, barley, wheat, pea, rice, millet, wrinkled peas, cassava, sago, tomato, oilseed rape, soy bean, hemp, flax, sunflower, cow-pea, arrowroot, clover, ryegrass, alfalfa, or maniok cell, in particular potato, wheat, maize or rice cell, comprising a nucleic acid molecule and/or a vector according to the invention.
The invention relates also to a process for the preparation of a transgenic host cell, preferably, a plant cell comprising the step of introducing a nucleic acid molecule and/or a vector of the invention into the genome of a host cell which is a procaryotic or eucaryotic cell, preferably, into the genome of a plant cell. Preferably, said cell contains a nucleic acid molecule which is linked to one or more regulatory elements which ensure transcription and/or translation in said cell. Suitable regulatory elements are preferably homologous or heterologous with respect to the nucleic acid molecule of the invention.
In another embodiment, the invention relates to a transgenic plant cell wherein the presence of a (homologous or optionally, heterologous) nucleic acid molecule of the invention leads directly or indirectly to the expression of the R1-protein of the invention or, alternatively, to the inhibition of the expression of one or more endogenous genes encoding an R1-protein. Preferably, the transgenic plant cell comprises a nucleic acid molecule which is selected from the group consisting of:
(a) a nucleic acid molecule of the invention, preferably a DNA molecule, which is transcribed into sense-RNA, which leads to the expression of an R1-protein of the invention;
(b) a nucleic acid molecule molecule of the invention, preferably a DNA molecule, which is transcribed into antisense-RNA which leads to the reduction (inhibition) of the expression of one or more endogenous genes encoding an R1-protein;
(c) a nucleic acid molecule molecule of the invention, preferably a DNA molecule, which is transcribed into a cosuppression-RNA (sense RNA) which leads to a reduction (inhibition) of the expression of one or more endogenous genes encoding an R1-protein;
(d) a nucleic acid molecule molecule of the invention, preferably a DNA molecule, which is transcribed into a ribozyme which specifically cleaves a transcript of one or more endogenous genes encoding an R1-protein; and
(e) a nucleic acid molecule of the invention which is introduced by in vivo mutagenesis, which modifies one or more endogenous genes encoding an R1-protein, hereby modifying starch metabolism/biosynthesis in said cell.
If the modification of starch metabolism in plants is achieved by means of an antisense effect, the DNA molecule of the invention is linked in antisense orientation with one or more regulatory elements ensuring the transcription and/or translation in a plant cell, optionally comprising one or more intron(s) of a corresponding genomic sequence of the polynucleotide to be expressed. The antisense RNA should exhibit a minimum of about 15-25 nucleotides, preferably at least about 50-100 nucleotides and most preferably at least about 200-1000 nucleotides.
In a further embodiment the decrease in the amount of an R1-protein in the transgenic plant cell is achieved by a ribozyme comprising a nucleic acid molecule of the invention. In order to express said ribozyme molecule in a transgenic plant cell of the invention, a DNA molecule encoding said ribozyme is linked to one or more regulatory elements which ensure transcription and/or translation.
By means of methods well known to the skilled person, the transgenic plant cell can be regenerated to a whole plant. The transgenic plant comprising a transgenic plant cell of the invention which is obtainable by regenerating the transgenic plant cell of the invention and the process for the preparation of said transgenic plant are also subject-matter of the present invention.
The transgenic plant of the invention is a monocotyledonous or dicotyledonous plant, preferably a crop plant, in particular a rye, barley, oat, rice, wheat, millet, sago, maize, pea, wrinkled pea, cassava, potato, tomato, maniok, oil seed rape, soy bean, hemp, flax, sunflower, cow-pea, white clover, ryegrass, alfalfa or arrowroot plant, most preferred a maize, wheat, rice, or potato plant.
Further the present invention relates to the propagation material, seed, organs, and parts of the plants of the invention.
The present invention also relates to a process for the production of starch comprising the step of introducing a transgenic plant cell, plant and/or part of a plant according to the invention into a process for the production/extraction of starch.
The present invention further relates to a process for the production of modified starch comprising the step of introducing a starch according to the invention into a process of chemical and/or physical modification/treatment of starch.
Processes for starch extraction from plants, plant cells, or parts thereof are well known in the art. Such processes are described, for example, in Eckhoff et al. (Cereal Chem. 73 (1996), 54-57). Extraction of maize starch is achieved by, e.g., xe2x80x9cwet-millingxe2x80x9d. Other methods for starch extraction from various plants are described, e.g., in Starch: Chemistry and Technology (eds.: Whistler, BeMiller and Paschall (1994) 2nd Edition, Academic Press Inc. London LTD; ISBN 0-12-746270-8; Chapter XII, page 417-468: Corn and Sorghum Starches: Production; by Watson, S. A.; Chapter XIII, page 469-479: Tapioca, Arrowroot and Sago Starches: Production by Corbishley and Miller; Chapter XIV, page 479-490: Potato Starch: Production and Uses; by Mitch; Chapter XV, page 491-506: Wheat starch: Production, Modification and Uses; by Knight and Olson; and Chapter XVI, page 507-528: Rice starch: Production and Uses; by Rohwer and Klem).
Means usually used in methods for the extraction of starches from plant materials are separators, decanters, hydroclones and different kinds of machines for drying the starch, e.g., spray drier or jet drier.
The present invention also relates to the modified starch obtainable from the transgenic plant cells, plants and/or parts of a plant of the invention, preferably from wheat. The transgenic cells or plants of the invention synthesize a modified starch which differs from a starch obtainable from non-transformed plants with respect to the degree of phosphorylation. In a specific embodiment of the invention, the starch according to the invention exhibits an increased phosphate content compared to a starch obtainable from corresponding non-transformed cells or plants. An increased phosphate content (phosphate-monoester content) means a starch containing about at least 10-30%, more preferably at least 30%, even more preferably at least 50%, and particularly preferred more than 100% up to about 1000-5000% increased phosphate content compared to the phosphate content of a starch obtainable from a corresponding non-transformed plant. In general, the percentage values refer to the glucose-6-phosphate (glu-6-P) content of wheat starch of about 0.3 nmol glu-6-P/mg starch determined, e.g., according to the method of Lim et al. Cereal Chem., (1994) 71, 448. Accordingly, the wheat starch according to instant invention comprises a glucose-6-phosphate content of at least 0.4 nmol/mg starch, preferably of at least 0.6 nmol/mg, more preferred at least 0.8 nmol/mg, in particular at least 1.0 nmol/mg, especially at least 1.5 nmol/mg, and most preferred at least 3.0 nmol/mg starch.
In another embodiment of the invention the starch of the invention exhibits a decreased phosphate content (phosphate-monoester content) of about at least 5-20%, preferably about at least 21-50%, even more preferably about 51-95% decreased phosphate content compared to the phosphate content of a starch obtainable from a corresponding non-transformed plant. Accordingly, the wheat starch according to instant invention exhibits a glucose-6-phosphate content of less than 0.2 nmol/mg starch, preferably less than 0.1 nmol/mg, more preferred less than 0.05 nmol/mg, in particular less than 0.02 nmol/mg, especially less than 0.01 nmol/mg, and most preferred less than 0.001 nmol/mg starch.
Another object of the invention is a method for the preparation of the R1-protein of the invention or derivative or part thereof comprising the steps of cultivating a transgenic host cell of the invention under conditions allowing for the expression of said R1-protein or derivative or part thereof and isolating said R1-protein or derivative or part thereof from said cells and/or the cultivating medium of said cells.
Furthermore, the invention relates to an R1-protein (R1-polypeptide) or derivative or part thereof encoded by the nucleic acid molecule of the invention obtainable by the method for the production of an R1-protein or derivative or part thereof according to the invention, preferably an R1-protein or derivative or part thereof derived from wheat, especially according to Seq. ID No. 2 and/or Seq. ID No. 10.
Within the present invention, the term xe2x80x9cregulatory element which ensures transcription and/or translationxe2x80x9d preferably has the meaning of a nucleic acid molecule (e.g., DNA and/or RNA) which allows for the initiation and/or termination of transcription in a cell, such as promoters, enhancers, terminators etc. The term xe2x80x9cregulatory element which ensures transcription and/or translationxe2x80x9d may also comprise a nucleic acid molecule which leads to a timely and/or locally (endosperm, root, tuber, leaf, stem, seed, fruit, apoplast, vacuole, cytosol, plastid, mitochondrium, lysosme) limited transcription within a plant/or plant cell or which is chemically inducible.
For the expression of the nucleic acid molecules of the invention in a plant cell any active promoter may be used. Said promoter may be homologous or heterologous with respect to the plant cell to be transformed, e.g., for constitutive expression the 35S promoter of the cauliflower mosaic virus (CaMV) (Odell et al., Nature 313 (1985), 810-812; Mitsuhara et al., Plant and Cell Physiology 37 (1996), 49-59) or the promoter construct described in WO 94/01571-A1. Suitable are also promoters which lead to a locally and/or timely limited expression determined/induced by endogenous and/or exogenous factors (e.g., WO 93/07279-A1), e.g., a limited expression with respect to a particular tissue or part of the plant (Stockhaus et al., EMBO J. 8 (1989), 2245-2251). Promoters which are active in the starch-storing part of the plant to be transformed are preferred. Preferred parts of plants are for the expression of the nucleic acid molecules of the invention, e.g., maize, wheat and rice grains or seeds and potato tubers and the like. For the transformation of potato the tuber-specific B33-promoter (Rocha-Sosa et al., EMBO J. 8 (1989), 23-29) may be used. Apart from promoters, DNA regions initiating transcription may also contain DNA sequences ensuring a further increase of transcription, such as the so-called enhancer-elements. For expression in plant cells, and in particular in wheat cells, the following promoters can be used: the 35S promoter (Odell et al. supra; Mitsuhara et al., supra), the ubiquitin promoter (U.S. Pat. No. 5,614,399, Christensen et al., Plant Mol. Biol. 18 (1992), 675-689; Takimoto et al., Plant Mol. Biol. 26 (1994), 1007-1012; Cornejo et al., Plant Mol. Biol. 23 (1993), 567-581; Toki et al., Plant Phys. 100 (1992), 1503-1507), glutelin promoter (Leisy et al., Plant Mol. Biol. 14 (1990), 41-50; Zheng et al., Plant J. 4 (1993), 357-366; Kononowicz et al., Joint annual meeting of The American Society of Plant Physiologists and The Canadian Society of Plant Pyhsiologists, Minneapolis, Minn., USA, Jul. 1 to Aug. 4, 1993, Plant Physiol. 102 (suppl.) (1993) 166; Zhao et al., Annual Meeting of the American Society of Plant Physiologists, Pittsburgh, Pa., USA, Aug. 1 to 5, 1992. Plant Physiol. 99 (1 Suppl.) (1992), 85; Yoshihara et al., FEBS Left. 383 (1996), 213-218, the actin promoter (McElroy et al., Plant Cell 2 (1990), 163-171), cab-6 promoter (Plant and Cell Physiology 35 (1994), 773-778), RTBV promoter (Yin et al., Plant J. 12 (1997), 1179-1188), CVMV promoter (Verdaguer et al., Plant Mol. Biol. 31 (1996), 1129-1139), rab 16B promoter (Plant Physiol. 112 (1996), 483-491), promoter of the psbD-C operon (To et al., Plant and Cell Physiology 37 (1996), 660-666), Tpi promoter (Snowden et al., Plant Mol. Biol. 31 (1996), 689-692), OsgrpI promoter (Xu et al., Plant Mol. Biol. 28 (1995), 455-471, Ltp2 promoter (Kalla et al., Plant J. 6 (1994), 849-860), ADH1 promoter (Kyozuka et al., Mol. Gen. Genet. 228 (1991), 40-48) and LHCP promoter (EMBO J. 10 (1991), 1803-1808).
Furthermore, the term xe2x80x9cregulatory elementxe2x80x9d also comprises a termination signal suitable to finalize the transcription and/or to add a poly-A-tail to the transcribed nucleic acid molecule. Examples for a termination signal are the 3xe2x80x2-nontranslatable regions comprising the polyadenylation signal of the nopaline synthase gene (NOS gene) or octopine synthase gene (Gielen et al., EMBO J. 8 (1989), 23-29) from agrobacteria, the 3xe2x80x2-nontranslatable region of the gene of the storage protein from soy bean or small subunit of ribulose-1,5-biphosphate-carboxylase (ssRUBISCO). Optionally, the term xe2x80x9cregulatory elementxe2x80x9d comprises a nucleic acid molecule which ensures, e.g., the specific location of transcription and/or translation of the nucleic acid molecule of the invention in a specific tissue (e.g., endosperm, leaf, stem, tuber, meristem, fruit, root, seed) or cell compartiment (e.g., cytosol, apoplast, plastid, mitochondrium, vacuole, lysosome). Optionally, the term xe2x80x9cregulatory elementxe2x80x9d comprises also nucleic acid molecules which ensures, e.g., timely limited transcription and/or translation of the nucleic acid molecule of the invention. Furthermore, the xe2x80x9cregulatory elementxe2x80x9d may optionally be chemically triggered.
The introduction of a nucleic acid molecule of the invention into a plant cell, preferably a DNA or RNA molecule, is generally carried out using cloning vectors which ensure stable integration of the nucleic acid molecule into the plant genome. In order to introduce a nucleic acid molecule into a higher plant a large number of cloning vectors are available containing a replication signal for E. coli and a marker gene for the selection of transformed bacterial cells, e.g., pBR322, pUC series, M13mp series, pACYC184. The nucleic acid molecule of the invention may be integrated into the vector at a suitable restriction site by use of one or more restriction endonuclease enzymes. The obtained plasmid is used for the transformation of, e.g., E. coli cells. Transformed cells are cultivated in a suitable medium and subsequently harvested and lysed, the plasmid DNA is recovered by means of standard methods and is generally analyzed by restriction and/or sequence analysis. After each manipulation the plasmid DNA may be cleaved and the obtained DNA fragments linked to other DNA sequences. In order to introduce DNA into a plant host cell a wide range of transformation methods and techniques are available, e.g., T-DNA transformation by use of Agrobacterium tumefaciens or Agrobacterium rhizogenes, fusion of protoplasts, injection of DNA, electroporation of DNA, and the introduction of DNA by membrane permeation (PEG) or means of the biolistic method and others. If whole plants are to be regenerated from transgenic plant cells, a selectable marker gene should be present. If the Ti- or Ri-plasmid is used, e.g., for transformation of the plant cell, at least the right border, preferably, the right and left border of the Ti- and Ri-plasmid T-DNA should be linked with the polynucleotide to be introduced into the plant cell as a flanking region. If Agrobacteria are used for transformation, the DNA to be introduced should be cloned into either an intermediate vector or binary vector. Due to sequence homologies to the sequences of the T-DNA, the intermediate vectors may be integrated into the Ti- or Ri-plasmid of the Agrobacterium by homologous recombination. Said intermediate vectors also contain the vir-region necessary for the transfer of the T-DNA. Since intermediate vectors cannot replicate in Agrobacteria, a helper plasmid may transfer the intermediate vector to Agrobacterium (conjugation). Binary vectors may replicate in E. coli and in Agrobacteria. They contain a selectable marker gene and a linker or polylinker which is flanked by the right and the left T-DNA border region. They may be transformed directly into the Agrobacteria (Holsters et al. Mol. Gen. Genet. 163 (1978), 181-187). The plasmids used for the transformation of Agrobacteria further comprise a selectable marker gene, e.g., the NPT II gene which allows for the selection of the transformed bacteria. The plasmid may comprise further selection marker genes e.g. conferring resistance against spectinomycin (Svab et al., Proc. Natl. Acad. Sci. U.S.A. 87 (1990), 8526-8530; Sval et al., Plant. Mol. Biol. 14 (1990), 197-206), streptomycin (Jones et al., Mol. Gen. Genet. 91 (1987), 86-91; Svab et al., Proc. Natl. Acad. Sci. U.S.A. 87 (1990), 8526-8530; Svab et al., Plant. Mol. Biol. 14 (1990), 197-206), phosphinothricine (De Block et al., EMBO J. 6 (1987), 2513-2518), glyphosate (Thompson et al., EMBO J. 6 (1987), 2519-2523; Thompson et al., Weed Sci. 35 (1987), 19-23 (suppl.)), or hygromycin (Waldron et al., Plant Mol. Biol. 5 (1985), 103-108). The Agrobacterium host cell should contain a plasmid carrying a vir-region. The vir-region is necessary for the transfer of the T-DNA into the plant cell. Additional T-DNA may be present. The transformed Agrobacterium is further used for the transformation of plant cells.
The use of T-DNA for the transformation of plant cells is described in EP-A-120 516; Hoekema, In: The Binary Plant Vector System Offsetdrukkerij Kanters B. V., Alblasserdam (1985), Chapter V; Fraley et al., Crit. Rev. Plant. Sci., 4, 146 and An et al., EMBO J. 4 (1985), 277-287. Binary vectors are commercially available, e.g., pBIN19 (Clontech Laboraties, Inc,, USA).
For transferring the DNA into the plant cells, plant explants may be co-cultivated with Agrobacterium tumefaciens or Agrobacterium rhizogenes. Whole plants may be regenerated from infected plant material (e.g., pieces of leaves, stem segments, roots, but also protoplasts or suspension-cultivated plant cells) in a suitable medium which allows for the selection of transformed cells (e.g., containing antibiotics or biocides etc.). The obtained plants are screened for the presence of the introduced DNA. Other possibilities in order to introduce foreign DNA by using, e.g., the biolistic method or by transforming protoplasts are known to the skilled person (e.g., Willmitzer, L., 1993 Transgenic plants. In Biotechnology, A Multi-Volume Comprehensive Treatise (H. J. Rehm, G. Reed, A. Pxc3xchler, P. Stadler, eds.), Vol. 2, 627-659, VCH Weinheim-New York-Basel-Cambridge).
The transformation of dicotyledonous plants by Ti-plasmid-vector systems by means of Agrobacterium tumefaciens is a well-established method. Agrobacteria can also be used for the transformation of monocotyledonous plants (Chan et al., Plant Mol. Biol. 22 (1993), 491-506; Hiei et al., Plant J. 6 (1994), 271-282).
Alternative methods for the transformation of monocotyledonous plants are, e.g., the transformation by means of the biolistic approach, protoplast transformation, electroporation of partially permeabilized cells, the introduction of DNA by means of glass fibers. Various references refer to the transformation of maize (WO 95/06128-A1, EP-A-0 513 849; EP-A-0 465 875). EP-A-292 435 describes a method how to obtain fertile plants starting from mucousless, friable granulous maize callus. Shillito et al. (Bio/Technology 7 (1989), 581) started from callus-suspension cultures which produce dividing protoplasts which are capable to regenerate to whole plants.
With regard to the transformation of wheat various methods can be applied, e.g., agrobacterium-medicated gene transfer (Hiei et al., Plant J. 6 (1994), 271-282; Hiei et al., Plant Mol. Biol. 35 (1997), 205-218; Park et al., J. Plant Biol. 38 (1995), 365-371), protoplast transformation (Data in xe2x80x9cGene transfer to plantsxe2x80x9d, I. Potrykus, G. Spangenberg (Eds.), Springer-Verlag Berlin Heidelberg, 1995, pages 66-75; Datta et al., Plant Mol. Biol. 20 (1992), 619-629; Sadasivam et al., Plant Cell Rep. (1994), 394-396) the biolistic approach (Li et al., Plant Cell Rep. 12 (1993), 250-255; Cao et al., Plant Cell Rep. 11 (1992), 586-591; Christou, Plant Mol. Biol. 81997), 197-203) and electroporation (Xu et al., in xe2x80x9cGene transfer to plantsxe2x80x9d, I. Potrykus, G. Spangenberg (Bds.), Springer-Verlag Berlin Heidelberg (1995), 201-208).
Once the introduced DNA has been integrated in the genome of the plant cell, it is usually stably integrated and remains within the genome of the descendants of the originally transformed cell. Usually the transformed cell contains a selectable marker gene which allows for the selections of the transformands in the presence of certain sugars, amino acids, biocids or antibiotics, e.g., kanamycin, G 428, bleomycin, hygromycin or phosphinothricine. Therefore, an individual marker gene allows for the selection of the transformed cells against cells lacking the introduced DNA.
After selection the transformed cells are cultivated under normal conditions and grow to a whole plant (McCormick et al., Plant Cell Reports 5 (1986), 81-84). The resulting plants can be cross-bred with plants having the same transformed genetic heritage or a different genetic heritage. Resulting individuals or hybrids have the corresponding phenotypic properties. Two or more generations should be grown in order to ensure whether the phenotypic feature is stable and transferable. Furthermore, seeds should be harvested in order to ensure that the corresponding phenotype or other properties will remain.
The modified starch obtainable from the plant cells, from the plants of the invention, or obtainable by the process of the invention is suitable for numerous industrial applications. Basically, starch can be subdivided into two major fields. One field comprises the hydrolysis products of starch, another the so-called native starches. The hydrolysis essentially comprise glucose and glucane components obtained by enzymatic or chemical processes. They can be used for further processes, such as fermentations and chemical modifications. Currently, starch hydrolysis is carried out substantially enzymatically using amyloglucosidase. Costs might be reduced by using lower amounts of enzyme for hydrolysis due to changes in the starch structure, e.g., increasing the surface of the grain, improved digestibility due to less branching or an altered steric structure, which limits the accesibility for the used enzymes. The use of the so-called native starch can be subdivided into the following areas:
(a) Use for the Preparation of Foodstuffs
Starch is a classic additive for various foodstuffs, wherein it essentially serves the purpose of binding aqueous additives and/or causes an increased viscositiy or an increased gel formation. Important characteristic properties are flowing and sorption behaviour, swelling and pastification temperature, viscositiy and thickening performance, solubility of the starch, transparency and paste structure, heat, shear and acid resistance, tendency to retrogradation, capability of film formation, resistance of freezing/thawing, digestibility as well as the capability of complex formation with , e.g., inorganic or organic ions.
(b) Use for the Preparation of Non-foodstuffs
The other major field of application is the use of starch as an adjuvant in various production processes or as an additive in technical products. The major fields of application for the use of starch as an adjuvant are, first of all, the paper and cardboard industry. In this field, the starch is mainly and for retention (holding back solids), for sizing filler and fine particles, as solidifying substance and for dehydration. In addition, the advantageous properties of starch with regard to stiffness, hardness, sound, grip, gloss, smoothness, tear strength as well as the surfaces are utilized.
Within the paper production process, a differentiation can be made between four fields of application, namely surface, coating, mass and spraying.
The requirement on starch with regard to surface treatment are essentially a high degree of brightness, corresponding viscosity, high viscosity stability, good film formation as well as low formation of dust. When used in coating the solid content, a corresponding viscosity, a high capability to bind as well as high pigment affinity play an important role. As an additive to the mass rapid, uniform, loss-free dispersion, high mechanical stability and complete retention in the paper pulp are of importance. When using the starch in spraying, corresponding content of solids, high viscosity as well as high capability to bind are also significant. A major field of application is, for instance, in the adhesive industry, where the fields of application are subdivided into four areas: the use as pure starch glue, the use in starch glues prepared with special chemicals, the use of starch as an additive to synthetic resins and polymer dispersions as well as the use of starches as extenders for synthetic adhesives. 90% of all starch-based adhesives are used in the production of corrugated board, paper sacks and bags, composits materials for paper and aluminium, boxes and wetting glue for envelopes, stamps, etc.
Another possible use as adjuvant and additive is in the production of textiles care products. Within the textile industry, a differentiation can be made between the following four fields of application: the use of starch as a sizing agent, i.e. as an adjuvant for smoothing and strengthening the burring behaviour for the protection against tensile forces active in weaving as well as for the increase of wear resistance during weaving as an agent for textile improvement mainly after quality-deteriorating pretreatments, such as bleaching dying, etc., as thickener in the production of dye pastes for the prevention of dye diffusion and as an additive for warping agents for sewing yarns.
Furthermore starch may be used as an additive in building materials. One example is the production of gypsum plaster boards, wherein the starch mixed in the thin plaster pastifies with the water, diffuses at the surface of the gypsum board and thus binds the cardboard to the board. Other fields of application are admixing it to plaster and mineral fibers. In ready-mixed concrete, starch may be used for the deceleration of the sizing process.
Furthermore, the starch is advantageous for the production of means for ground stabilization used for the temporary protection of ground particles against water in artificial earth shifting. According to state-of-the-art knowledge, combination products consisting of starch and polymer emulsions can be considered to have the same erosion- and encrustation-reducing effect as the products used so far; however, they are considerably less expensive.
Another field of application is the use of starch in plant protectives for the modification of the specific properties of these preparations. For instance, starches are used for improving the wetting of plant protective and fertilisers, for the dosed release of the active ingredients, for the conversion of liquid, volatile and/or odorous active ingredients into microcristalline, stable, deformable substances, for mixing incompatible compositions and for the prolongation of the duration of the effect due to a reduced disintegration.
Starch may also be used in the fields of drugs, medicine and in the cosmetics industry. In the pharmaceutical industry, the starch may be used as a binder for tablets or for the dilution of the binder in capsules. Furthermore, starch is suitable as disintegrant for tablets since, upon swallowing, it absorbs fluid and after a short time it swells so much that the active ingredient is released. It is also a suitable auxiliary to achieve a time-delayed release of the active ingredient (retardation effect). For qualitative reasons, medicinal flowance and dusting powders are further fields of application. In the field of cosmetics, the starch may for example be used as a carrier of powder additives, such as scents and salicylic acid. A relatively extensive field of application for the starch is toothpaste.
The use of starch as an additive in coal and briquettes is also suitable. By adding starch, coal can be quantitatively agglomerated and/or briquetted in high quality, thus preventing premature disintegration of the briquettes. Barbecue coal contains between 4 and 6% added starch, calorated coal between 0.1 and 0.5%. Furthermore, the starch is suitable as a binding agent since adding it to coal and briquette can considerably reduce the emission of toxic substances.
Furthermore, the starch may be used as a flocculant in the processing of ore and coal slurry.
Another field of application is the use as an additive to process materials in casting.
For various casting processes cores produced from sands mixed with binding agents are needed. Nowadays, the most commonly used binding agent is bentonite mixed with modified starches, mostly swelling starches.
The purposes of adding starch is increased flow resistance as well as improved binding strength. Moreover, swelling starches may fulfill more prerequisites for the production process, such as dispersability in cold water, rehydratisability, good mixability in sand and high capability of binding water.
In the rubber industry starch may be used for improving the technical and optical quality. Reasons for this are improved surface gloss, grip and appearance. For this purpose, the starch is dispersed on the stickly rubberized surfaces of rubber substances before the cold vulcanization. It may also be used for improving the printability of rubber.
Another field of application for the modified starch is the production of leather substitutes.
In the plastics market the following fields of application are emerging: the integration of products derived from starch into the processing process (starch is only a filler, there is no direct bond between synthetic polymer and starch) or, alternatively, the integration of products derived from starch into the production of polymers (starch and polymer form a stable bond).
The use of the starch as a pure filler cannot compete with other substances such as talcum. This situation is different when the specific starch properties become effective and the property profile of the end products is thus clearly changed. One example is the use of starch products in the processing of thermoplastic materials, such as polyethylene. Thereby, starch and the synthetic polymer are combined in a ratio of 1:1 by means of coexpression to form a master batch, from which various products are produced by means of common techniques using granulated polyethylene. The integration of starch in polyethylene films may cause an increased substance permeability in hollow bodies, improved water vapor permeability, improved antistatic behaviour, improvied antiblock behaviour as well as improved printability with aqueous dyes.
Another possibility is the use of the starch in polyurethane foams. Due to the adaption of starch derivatives as well as due to the optimization of processing techniques, it is possible to specifically control the reaction between synthetic polymers and the starch""s hydroxy groups. The results are polyurethane films having the following property profiles due to the use of starch: a reduced coefficient of thermal expansion, decreased shrinking behaviour, improved pressure/tension behaviour, increased water vapor permeability without a change in water acceptance, reduced flammability and cracking density, no drop off of combustible parts, no halides and reduced aging. Disadvantages that presently still exists are reduced pressure and impact strength.
Product development of film is not the only option. Also solid plastics products, such as pots, plates and bowls can be produced by means of a starch content of more than 50%. Furthermore, the starch/polymer mixtures offer the advantage that they are much easier biodegradable.
Furthermore, due to their extreme capability to bind water, starch graft polymers have gained utmost importance. These are products having a backbone of starch and a side lattice of a synthetic monomer grafted on according to the principle of radical chain mechanism. The starch graft polymers available nowadays are characterized by an improved binding and retaining capability of up to 1000 g water per g starch at a high viscosity. These super absorbers are used mainly in the hygiene field, e.g., in products such as diapers and sheets, as well as in the agricultural sector, e.g., in seed pellets.
Deposit of Biological Material
The following plasmids as described in the present invention were deposited in accordance with the requirements of the Budapest Treaty at the Deutsche Sammlung fur Mikroorganismen und Zellkulturen (DSMZ) in Braunschweig, Germany: Plasmid pTaR1-11 refers to accession number DSM No. 12810 at May 20, 1999. Plasmid RS26-88 refers to accession number DSM No. 13511 at May 24, 2000.
The following Examples shall merely illustrate the invention and do not limit the invention in any way.